Current trends indicate an increasing demand worldwide for high quality, low residual content metals. In one conventional method, a metal, particularly steel, may be refined in a furnace by providing the metal in a liquid state and adding molten slag thereto. Impurities in the metal are thereby chemically reduced and retained in the molten slag. The amount of impurities removed from the slag and the rate of removal is primarily limited by the amount of slag used and the capacity of the slag for the impurities.
M.G. Frohberg, M.L. Kapoor, and A. Nilas in the article entitled "Review Paper: Desulphurization", J.I.S.I., Feb. 1965, pp. 139-182 suggest using methods such as mechanical stirring and adjustment of the oxygen potential to improve the removal of sulphur from steel.
In the article "The Kinetics of Sulphur Transfer from Iron to Slag", R.G. Ward and K.A. Salmon, J.I.S.I., Dec. 1960, pp. 393-402, the electrolytic nature of sulphur transfer is discussed. In another article by the same workers, "The Kinetics of Sulphur transfer from Iron to Slag", J.I.S.I., Mar. 1963, pp. 222-227, the use of electrolytic methods to enhance sulphur removal using a current density below which arcing occurs is investigated. It was concluded that the process was too inefficient to be commercially attractive.
It is known to refine certain metals using solely an electrolytic process. However, a very large amount of electricity must be used which often renders this process prohibitively expensive. It is also known to refine certain metals in their molten state by reacting them with a second phase, such as slag. Accordingly, it would be desirable to have a process whereby the two above-mentioned technologies could be economically combined.
Alloying of liquid metals conventionally requires the separate step of converting the oxides of the alloy to be added into a reduced form of the alloy which can then be added to the liquid metal. In the case of chromium alloys for steel, the chromium oxide must be converted to ferrochromium. This process tends to be very expensive. Accordingly, it would be desirable to have a process whereby the oxides of the alloy could be converted to their reduced form in a relatively simple and economical manner.
It is an object of the present invention to obviate or mitigate the above-mentioned disadvantages.